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Keywords:

  • dwarf sperm whale;
  • pygmy sperm whale;
  • Kogia breviceps;
  • Kogia sima;
  • mtDNA;
  • control region;
  • cytochrome b;
  • phylogeny;
  • cetaceans

Abstract

Concordance between mitochondrial DNA (mtDNA) markers and morphologically based species identifications was examined for the two currently recognized Kogia species. We sequenced 406 base pairs of the control region and 398 base pairs of the cytochrome b gene from 108 Kogia breviceps and 47 K. sima samples. As expecred, the two sister species were reciprocally monophyletic to each other in phylogenetic reconstructions, but within K. sima, we unexpectedly observed another reciprocally monophyletic relationship. The two K. sima clades resolved were phylogeographically concordant with all of the haplotypes in one clade observed solely among specimens sampled from the Atlantic Ocean and with those in the other clade observed solely among specimens sampled from the Indo-Pacific Ocean. These apparently allopatric clades were observed in all phylogenetic reconstructions using the maximum parsimony, maximum likelihood, and neighborjoining algorithms, with the mtDNA gene sequences analyzed separately and combined. The nucleotide diversity for the combined gene sequence haplotypes of the two K. sima clades resolved in our analyses was 0.58% and 1.03% for the Atlantic and Indo-Pacific, respectively, whereas for the two recognized sister species, nucleotide diversity was 1.65% and 4.02% for K. breviceps and K. sima, respectively. The combined gene sequence haplotypes have accumulated 44 fixed base pair differences between the two K. sima clades compared to 20 fixed base pair differences between the two recognized sister species. Although our results are consistent with species-level differences between the two K. sima clades, recognition of a third Kogia species awaits supporting evidence that these two apparently allopatric clades represent reproductively isolated groups of animals.